A large majority of electronic circuits require one or more power supplies for operation. It is a requirement that the power supplies be stable. However, even though the power supplies are considered stable, the power supply levels generated for some applications usually vary during operation. For instance, a 3.3 volt power supply may generate anywhere from 2.8 volts to 3.7 volts during its operation and still be considered a 3.3 volt power supply. Similarly, a 5 volt power supply may generate anywhere from 4.2 to 5.6 volts during its operation and still be considered a 5 volt power supply. These varying type of power supplies are employed in powering electronic circuitry on computer chips.
Today, certain computer chips are capable of operating with two different power supply levels. For instance, a chip may be able to operate using either a 5 volt or a 3.3 volt power supply. Furthermore, certain chips in the market today utilize different power supply levels for different portions of the chip. In other words, a portion of the chip may be powered by a power supply at one level (e.g., 5 volt supply), while another portion of the chip is powered by a power supply at a different level (e.g., 3.3 volt supply). Also a portion of the chip may be powered by a power supply at one level (e.g., 3.3 volt supply), while another portion of the chip is capable of operating at more than one power supply level (e.g., 3.3 volts or 5 volts).
Some of the circuitry on these dual or multi-power supply level chips are sensitive to the power supply level under which they operate. In these instances, the circuits must be programmed according to the power supply level which is being utilized. In the prior art, these circuits are programmed in one of two ways. First, a set of registers located on the chip itself is available for the user to program the level of the power supply currently being used. Depending on how the user programs the register, the circuitry is able to compensate for the various power supplies levels which can be received. However, the use of registers on-chip requires the use of memory storage on-chip. Memory storage is limited on-chip and generally there is a need to limit the use of on-chip memory. Furthermore, the use of these on-chip registers requires the time of a system designer to program them.
Second, external pins may be used to indicate to the chip the level of the power supply being used. For instance, when a single pin is used to indicate the power supply level for a chip, the chip is capable of operating at two different power supply levels. When the pin is in one state (e.g., a logical 0), the power supply level is at a first level, while if the pin is at the other state (e.g., a logical 1), then the power supply is at a second level. If multiple portions of a chip are capable of operating at different power levels, then each separate portion would require a separate pin. The number of pins on a chip directly affects the size of the chip. The more pins a chip has, the larger it is. To minimize the chip size, the number of pins must be reduced. Thus, there is a need to allow a chip, or portion thereof, to be powered by more than one power supply level, while keeping the pin count down.
As will be shown, the power supply level detector of the present invention eliminates the need to have on-chip programmable registers to indicate to the chip the power supply level. Also the power supply level detector of the present invention eliminates the need to use external pins to program circuitry requiring knowledge of the power supply level to operate correctly. The power supply level detector of the present invention determines the level of the power supply and generates a signal indicative of that level.